DGS Annual Report

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Site content related to keyword: "Columbia aquifer"

DGS participates in inter-agency meeting on Chesapeake Watershed

DGS staff member A. Scott Andres made a presentation “Results of selected UD nutrient monitoring projects in the Nanticoke River watershed” at the inter-agency meeting Chesapeake basin water quality data, trends, and interpretations held August 11, 2016 at the Delaware Department of Agriculture in Dover.

Journal article "Hydrogeologic controls on groundwater discharge and nitrogen loads in a coastal watershed"

A recently released article “Hydrogeologic controls on groundwater discharge and nitrogen loads in a coastal watershed” by the Journal of Hydrology details the results of a joint groundwater simulation and water quality sampling study that focused on submarine groundwater discharge (SGD) to Indian River and Rehoboth Bays, part of Delaware Inland Bays.

Delaware Geological Survey Issues Report on Wastewater Treatment used for Rapid Infiltration Basin Systems

The Delaware Geological Survey released a new technical report entitled “Evaluation Of Wastewater Treatment Options Used In Rapid Infiltration Basin Systems (RIBS)” which was prepared by Müserref Türkmen of the Izmir Water and Sewearge Administration, Turkey, A. Scott Andres of the Delaware Geological Survey, Edward Walther of the South Water Management District, Florida, and William Ritter and Anastasia Chirnside of the University’s College of Agriculture and Natural Resources. DGS Bulletin 21A documents the results of a detailed study of wastewater treatment plant technologies and effectiveness of treatment types that are used to treat wastewater prior to disposal into the ground by rapid infiltration basin systems.

RI79 Simulation of Groundwater Flow and Contaminant Transport in Eastern Sussex County, Delaware With Emphasis on Impacts of Spray Irrigation of Treated Wastewater

Simulation of Groundwater Flow and Contaminant Transport in Eastern Sussex County, Delaware With Emphasis on Impacts of Spray Irrigation of Treated Wastewater

This report presents a conceptual model of groundwater flow and the effects of nitrate (NO3-) loading and transport on shallow groundwater quality in a portion of the Indian River watershed, eastern Sussex County, Delaware. Three-dimensional, numerical simulations of groundwater flow, particle tracking, and contaminant transport were constructed and tested against data collected in previous hydrogeological and water-quality studies.

The simulations show a bimodal distribution of groundwater residence time in the study area, with the largest grouping at less than 10 years, the second largest grouping at more than 100 years, and a median of approximately 29 years.

Historically, the principal source of nitrate to the shallow groundwater in the study area has been from the chemical- and manure-based fertilizers used in agriculture. A total mass of NO3- -nitrogen (N) of about 169 kg/day is currently simulated to discharge to surface water. As the result of improved N-management practices, after 45 years a 20 percent decrease in the mass of NO3- -N reaching the water table would result in an approximately 4 percent decrease in the mass of simulated N discharge to streams. The disproportionally smaller decrease in N discharge reflects the large mass of N in the aquifer coupled with long groundwater residence times.

Currently, there are two large wastewater spray irrigation facilities located in the study domain: the Mountaire Wastewater Treatment Facility and Inland Bays Wastewater Facility. The effects of wastewater application through spray irrigation were simulated with a two-step process. First, under different operations and soil conditions, evaporation and water flux, NO3- -N uptake by plants, and NO3- -N leaching were simulated using an unsaturated flow model, Hydrus-1D. Next, the range of simulated NO3- -N loads were input into the flow and transport model to study the impacts on groundwater elevation and NO3- -N conditions.

Over the long term, the spray irrigation of wastewater may increase water-table elevations up to 2.5m and impact large volumes of groundwater with NO3-. Reducing the concentration of NO3- in effluent and increasing the irrigation rate may reduce the volumes of water impacted by high concentrations of NO3-, but may facilitate the lateral and vertical migration of NO3-. Simulations indicate that NO3- will eventually impact deeper aquifers. An optimal practice of wastewater irrigation can be achieved by adjusting irrigation rate and effluent concentration. Further work is needed to determine these optimum application rates and concentrations.

Drought Conditions Indicators for Delaware

Summary of Water Conditions for Delaware website screen shot for March 2015

The DGS will research past performance of the Water Conditions Index (WCI) for Northern New Castle County, as compared with other established drought indicators, and investigate modifying the WCI, if needed. We will also investigate the feasibility of quantifying water conditions in Kent and Sussex Counties by analyzing factors that are most important to these regions (i.e., precipitation, groundwater for agricultural irrigation, etc….)

Data and Graphs of Water Level Summaries for Wells with 20+ Years or 100+ Observations

Example Hydrograph for DB24-18 - Water Level Summaries for Wells with 20+ Years or 100+ Observations

Ground-water levels are basic information needed for evaluating water conditions and for basic and applied research. For these efforts, water levels are being measured statewide in wells completed in multiple aquifers. Some wells are measured for specific projects, such as the Coastal Aquifers Salinity Project and the Water Conditions program, while other wells are measured so that staff can maintain long term records of ground-water levels for evaluation of trends. Table contains summary data from wells having 100 or more water level observations.

Water Level Summaries for DGS Index Wells

Locations of DGS Index Wells throughout Delaware

Groundwater levels are basic information needed for evaluating water conditions and for basic and applied research. For these efforts, water levels from various aquifers are being measured statewide. Some wells are measured for specific reasons, such as for the Coastal Aquifers Salinity Project and the Water Conditions Report, while other wells are measured so that staff can maintain long-term records of groundwater levels for evaluation of trends.

RI78 Subsurface Geology of the Area Between Wrangle Hill and Delaware City, Delaware

RI78 Subsurface Geology of the Area Between Wrangle Hill and Delaware City, Delaware

The geology and hydrology of the area between Wrangle Hill and Delaware City, Delaware, have been the focus of numerous studies since the 1950s because of the importance of the local groundwater supply and the potential environmental impact of industrial activity. In this report, 490 boreholes from six decades of drilling provide dense coverage, allowing detailed characterization of the subsurface geologic framework that controls groundwater occurrence and flow.

The region contains a lower section of tabular Cretaceous strata (Potomac, Merchantville, Englishtown, Marshalltown,and Mount Laurel Formations in ascending order) and a more stratigraphically complex upper section of Pleistocene-to-modern units (Columbia, Lynch Heights, and Scotts Corners Formations, latest Pleistocene and Holocene surficial sediments and estuarine deposits). The lowermost Potomac Formation is a mosaic of alluvial facies and includes fluvial channel sands that function as confined aquifer beds; however, the distribution of aquifer-quality sand within the formation is extremely heterogeneous. The Merchantville Formation serves as the most significant confining layer. The Columbia Formation is predominantly sand and functions as an unconfined aquifer over much of the study area.

To delineate the distribution and character of the subsurface formations, densely spaced structural-stratigraphic cross sections were constructed and structural contour maps were created for the top of the Potomac Formation and base of the Columbia Formation. The Cretaceous formations form a series of relatively parallel strata that dip gently (0.4 degrees) to the southeast. These formations are progressively truncated to the north by more flatly dipping Quaternary sediments, except in a narrow north-south oriented belt on the east side of the study area where the deeply incised Reybold paleochannel eroded into the Potomac Formation.

The Reybold paleochannel is one of the most significant geological features in the study area. It is a relatively narrow sandfilled trough defined by deep incision at the base of the Columbia Formation. It reaches depths of more than 110 ft below sea level with a width as narrow as 1,500 ft. It is interpreted to be the result of scour by the sudden release of powerful floodwaters from the north associated with one or more Pleistocene deglaciations. Where the Reybold paleochannel cuts through the Merchantville confining layer, a potential pathway exists for hydrological communication between Columbia and Potomac aquifer sands.

East of the paleochannel, multiple cut-and-fill units within the Pleistocene to Holocene section create a complex geologic framework. The Lynch Heights and Scotts Corners Formations were deposited along the paleo-Delaware River in the late Pleistocene and are commonly eroded into the older Pleistocene Columbia Formation. They are associated with scarps and terraces that represent several generations of sea-level-driven Pleistocene cut-and-fill. They, in turn, have been locally eroded and covered by Holocene marsh and swamp deposits. The Lynch Heights and Scotts Corners Formations include sands that are unconfined aquifers but complicated geometries and short-distance facies changes make their configuration more complex than that of the Columbia Formation.

Delaware Geologic Information Resource (DGIR) Map Viewer

DGIR Map Viewer Screenshot
Project Contact(s):

The Delaware Geologic Information Resource (DGIR) is an online data display tool and map viewer for a variety of geologic and hydrologic information released by the Delaware Geological Survey. It was designed to deliver the most commonly available and requested geologic and hydrologic information that is appropriate for use in hydrologic studies, required by regulation and ordinance, and to support state resource management decisions.

Effect of tropical storms Irene and Lee on groundwater levels in well Qb35-08

Plot of groundwater levels, groundwater temperature, and rainfall near Laurel, Delaware

Tropical storms Irene and Lee caused a 9-1/2 foot rise of the water table in western Sussex County near Laurel. Groundwater levels and temperatures in Qb35-08 were collected with an automated pressure-temperature datalogger system. At the same time, rainfall and soil moisture data were recorded by the DEOS Laurel Airport station located approximately 5 miles from the well.

Delaware Groundwater Monitoring Network

The Delaware Geological Survey (DGS) currently monitors groundwater levels in a network of 68 wells in Delaware. Long time-series of water levels in major aquifers serve as critical baseline data for resource management and analyses of aquifer response to pumping, climatic variability, drought hazards, seawater intrusion, and interaction with streams and their ecosystems.

DGS issues report on groundwater modeling in southern New Castle County

The Delaware Geological Survey (DGS) released a new technical report entitled Simulation of Groundwater Flow in Southern New Castle County, Delaware, which was prepared by Changming He and A. Scott Andres of the DGS.

DGS Report of Investigations No. 77 is a preliminary step in developing a detailed understanding of the subsurface hydrology and evaluating groundwater availability in major aquifer systems beneath southern New Castle County and parts of northern Kent County, which are expected to have greater demands for groundwater in the next 20 years due to population growth.

RI77 Simulation of Groundwater Flow in Southern New Castle County, Delaware

RI77 Simulation of Groundwater Flow in Southern New Castle County, DelawareRI77 Simulation of Groundwater Flow in Southern New Castle County, Delaware

To understand the effects of projected increased demands on groundwater for water supply, a finite-difference, steady-state, groundwater flow model was used to simulate groundwater flow in the Coastal Plain sediments of southern New Castle County, Delaware. The model simulated flow in the Columbia (water table), Rancocas, Mt. Laurel, combined Magothy/Potomac A, Potomac B, and Potomac C aquifers, and intervening confining beds. Although the model domain extended north of the Chesapeake and Delaware Canal, south into northern Kent County, east into New Jersey, and west into Maryland, the model focused on the area between the Chesapeake and Delaware Canal, the Delaware River, and the Maryland-Delaware border. Boundary conditions for these areas were derived from modeling studies completed by others over the past 10 years.

Compilation and review of data used for model input revealed gaps in hydraulic properties, pumping, aquifer and confining bed geometry, and water-level data. The model is a useful tool for understanding hydrologic processes within the study area such as horizontal and vertical flow directions and response of aquifers to pumping, but significant data gaps preclude its use for detailed analysis for water resources management including estimating flow rates between Delaware and adjacent states. The calibrated model successfully simulated groundwater flow directions in the Rancocas and Mt. Laurel aquifers as expected from the conceptual model. Flow patterns in the Rancocas and Mt. Laurel aquifers are towards local streams, similar to flow directions in the Columbia (water table) aquifer in locations where these aquifers are in close hydraulic connection.

Water-budget calculations and simulated heads indicate that deep confined aquifers (Magothy and Potomac aquifers) receive groundwater recharge from shallow aquifers (Columbia, Rancocas, and Mt. Laurel aquifers) in most of the study domain. Within shallow aquifers, groundwater moves toward major streams, while in the deep aquifers, groundwater moves
toward major pumping centers.

The Delaware Water Conditions Summary

The Water Conditions Summary is an online monthly summary of water conditions in Delaware. Principal factors in determining water conditions are precipitation, streamflow, and groundwater levels in aquifers. Data from rain gages, stream gages, and observation wells located throughout Delaware have been collected and compiled since the 1960s by the Delaware Geological Survey. These data are displayed as hydrographs and are also available for download. In general, water is abundant in Delaware, but supply is restricted by natural geologic conditions in some areas, by contamination in others, and is dependent on precipitation.

Web-Delivered Application for Hydrogeologic Data

Project Contact(s):

This project is designed to deliver, by web-based technologies, the most commonly available and requested geologic and hydrologic information used in hydrologic studies required by regulation and ordinance and used by state agencies to support resource-management decisions. Available information can be associated with points or areas. Information associated with points includes descriptive logs, geophysical logs, raw and interpreted groundwater levels, aquifer and geologic unit identification, and hydraulic characteristics of wells. Information associated with areas is either in the form of raster-based (grid) data or polygons. Examples of raster-based data include water-table depths and elevations, tops and thicknesses of geologic and aquifer units, and aquifer transmissivity. Examples of polygons include surficial geology and groundwater recharge potential.

The intent of developing a web-technology enabled system is to provide a more intuitive and comprehensive toolset for locating, quickly viewing, and downloading the desired information in an efficient, extensible, and familiar manner.

Quantifying Geologic and Temporal Controls on Water and Chemical Exchange between Groundwater and Surface Water in Coastal Estuarine Systems

Conceptual models for submarine groundwater discharge
Project Contact(s):

Eutrophication is one of the most common and most severe problems facing coastal bays in
populated and agricultural areas. Unnaturally high quantities of nutrients enter fresh groundwater and surface water as a result of human activities. These nutrients contribute to the overpopulation of phytoplankton and macroalgae in coastal surface waters, which results in deterioration of water quality and animal habitat. This is a particular problem in the Delmarva region, where poultry farms, agricultural activity, and growing human populations have contributed to rapidly declining populations of blue crabs, striped bass, and many other species which live and breed in estuarine waters. The economic value of these species has, in part, prompted political action and efforts to manage nutrient inputs to groundwater and surface water, the primary pathways for nutrient loading to coastal waters. Despite significant reductions, coastal water quality has largely remained poor. A better understanding of the processes that moderate nutrient loading to coastal waters, particularly via groundwater, which is much more difficult to monitor than surface water inputs, is essential for improved management methods that will result in healthy coastal ecosystems. This project will improve understanding of where nutrients are coming from and how loading may be reduced, and may aid in identification of activities that exacerbate negative impacts.